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  #1 (permalink)  
Old 27th May, 2004, 11:19 PM
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Question Which way should a fan blow?

I just recently bought a window case and I'm installing 4 fans (2 rear fans, and 2 lower side panel fans) I was wondering which way the direction of the air is best. I know it has always (or at least it seems to me) been that the fans take out hotter air instead of blowing cooler in, but I was wondering if it would be better to blow the cool air in. Or if the 2 side fans should push in cool air and the rear fans take out hot air and that way it would circulate air throughout the case. But I am not sure which really does provide better cooling. Any suggestions?
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Old 28th May, 2004, 12:05 AM
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I am hooking the fans up now and confused at which way to face them.......lol
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Old 28th May, 2004, 01:06 AM
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You want to have a push pull configuration, i.e 2 on the rear as exaust and 2 on the front/side as intake. This will help to get good airflow though the case.

Installing all fans to blow air out will cause a negative case preasure which means air and dust will be sucked in through every crack and gap resulting is a messy dusty looking case, if you look at some older systems that have maybe 1 rear fan as exaust you'll see allot of dust buildup on the PCI expansion slots and the ATX backplate.

Installing filters on the intake fans will greatly reduce system 'muck'.
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Old 28th May, 2004, 02:28 AM
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Too late . I just finished installing the fans and all are blowing air in. It is REALLY cold in there now. I'll see how this works out for me, but thanks!
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Old 28th May, 2004, 05:03 AM
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yea well I would of had 2 blowing in and ht other 2 out. With the side nes blowing in. (several reasons- so air is nt blowing out on the side and so that thye are blowingair in and across the mobo.
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Old 28th May, 2004, 03:31 PM
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I'm sure dust is going to become a MAJOR factor/problem in this setup b/c all air is blowing in, but I'm too lazy to turn them all around (or even 2 of them)......lol
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Old 6th June, 2004, 07:25 PM
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Hi

The idea is to have intake fans bringing external air into your case and having an equivalent volume of air being exhausted from the case. If you do not have exhaust fans blowing the air out, then much of the air will circulate inside the case, becoming warmer and horribly reducing any cooling.


As warm air typically rises above cool air, it's recommended that the intake fans are placed in lower spots and that exhaust fans are placed higher up. This is why folks tend to place intake fans near the lower front of the case (and this is also the reason that newer cases have fan-mounts there).

Since the heated air tends to rise and the CPU generates a lot of air, the PSU's fan generally exhausts air. Additional fans mounted in the spots directly below the PSU should exhaust the warm air that builds up in the space around the CPU. An effective place to exhaust heat, is through a blowhole in the top of the case with a fan pulling the air out.

Now: if you do want to have side-panel fans, it's highly recommendable to mount the fans as intakes and to have them blowing as close as possible to the CPU.

On to the dust issue... Having filters of some kind over the intake fans is a very good idea. But this is not the sole source of dust. Unless your case is perfectly sealed, there are numerous places where dust can flow and this is a very important fact.

If you only have intake fans, your fans will be the main source of dust intake. But, the air will escape through any spaces in the case. This is known as a positive pressure case, since after switching the PC on, the air pressure inside the case will start off being higher than the pressure outside the case. So if you control the dust being brought in at the fans, then your case will have less dust than most.


If the exhaust fans push out more air than the intake fans are bringing in, then air pressure laws will cause air to flow in through the other spaces. This is referred to as a negative pressure situation and will lead to dust being sucked in as well, since it's hard to prevent if the case is not carefully and effectively sealed.

Thus, for most of us normal case owners, the trade-off is between good cooling (which requires a balance between the cool air being brought in and the warm air being exhausted), and minimising the dust being sucked in (which is done through filters and/or a positive internal pressure).


I hope that all helped to clarify a few issues
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Old 6th June, 2004, 09:37 PM
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i always have positive pressure in my case....when i take my door off my temps go up 4 degrees.
i have 2 Tt smartfans @ 3000rpm intake and one generic 2500rpm fan intake
i Tt smartfan exhaust @ 3750rpm and psu @ 1450rpm.
yes i get alot of dust...to the point that i buy canned air by the dozen.
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Old 7th June, 2004, 09:15 AM
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cadaveca: Do you have filters over your intakes?

I would expect that having a positive (internal) pressure would mean that mainly your fans are pulling the dust in, as the air will be trying to exit through the spaces in your case and therefore minimising the dust intake.
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Old 7th June, 2004, 05:33 PM
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actualy...having positive pressure leads to lots of dust bulidup on th e intake fans themselves...but not so bad once inside the case.
i get a visible layer of dust on the fans within 2 days(the pc runs 24/7)
no dust screens...i was changing them every week...now i blow with air every 10 days..and alwaya get a 2c drop in temps when done.
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Old 7th June, 2004, 06:03 PM
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cadaveca, does your case have a fair amount of grills for air to escape?

AFAIK it is possible to create a dust free system by using the positive method. But this does involve using high CFM fans and fine filters which would need regular cleaning.
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Old 7th June, 2004, 06:15 PM
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and it's the regular cleaning that i am not about to undertake....i mean i got as much as 180cfm going in my case....and the back panel is nothing but holes.
i pulled the door off to give it some air today, and got a 3c raise in temps upon door removal....the dust is slightly problematic, especially with my vid card overclocked 135mhz adn the fan on the vid card is the worst for dust because it is so small.
i've tried other combo's of in/out and negative pressure...but because i have a long hair cat, negative pressure is not good here.i have 56c @ full load wether door's on or off(readin from on-die sensor)...case temps will fluctuate with the door.
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Old 7th June, 2004, 06:28 PM
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Thanks!

I'm going to be reworking my case fan situation in the near future and I'm exploring all the possiblities first. Negative is definately off the cards. Positive is looking good.
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Old 7th June, 2004, 06:41 PM
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positive pressure works well for me...it seems to keep alot of the humidity out of my case as well. the dust is ok to deal with...as I am in the progress of doing a mod, i am always in the case
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Old 24th June, 2004, 06:41 PM
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I can only fit two fans in my case next to each other (one above the other) is it best to have one blowing out and one blowing in??
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Old 24th June, 2004, 07:10 PM
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Quote:
Originally Posted by matte
I can only fit two fans in my case next to each other (one above the other) is it best to have one blowing out and one blowing in??
No, they must be both working in the same direction if they are next to each other. Otherwise the intake fan will draw air from the exhaust fan.
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Old 24th June, 2004, 07:57 PM
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I have my side fan sucking air in. My antec plusview has it situated right over my graphics card which is great for cooling the ramsinks I added to it. What this does for the internal airflow I don't know, but I have 2 fans on the front blowing air over two of my three hard drives, the other just at the bottom of the case. I have another low rpm facing upwards blowing the cold air to the top of the case where the cpu is. From here it is sucked out by two more fans and the PSU fans. Seems to work well, my case temps rarely go above 35'c with the room usually around 25'c. This is with all fans on lowrpm via my zalman 6fan controller.
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Old 24th June, 2004, 09:05 PM
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Quote:
Originally Posted by danrok
No, they must be both working in the same direction if they are next to each other. Otherwise the intake fan will draw air from the exhaust fan.
Both intake or both exhaust??
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Old 24th June, 2004, 11:16 PM
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Quote:
Originally Posted by matte
Both intake or both exhaust??
Both as intakes would be the norm.
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Old 24th June, 2004, 11:19 PM
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Quote:
Originally Posted by danrok
Both as intakes would be the norm.
Thanks
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